The single-ended primary inductance convertor or SEPIC is a well-known DC-to-DC voltage convertor that can provide an output voltage greater or less than an input voltage. It also does not change or reverse an input voltage polarity. A detailed explanation of SEPICs is available from Daniel W. Hart, Power Electronics, McGraw-Hill Companies, Inc., 2011, pages 231-235, the content of which is incorporated herein by reference.
Referring now to FIG. 1, a SEPIC 100 needs a switch 24, typically embodied as a metal oxide semiconductor field effect transistor (MOSFET) to charge and discharge inductors 22, 28 and capacitors 26 and 32 as described by Hart, supra. The SEPIC output voltage i.e., Vout is the function of the input voltage, Vin and a duty ratio of the switch in Continuous Conduction Mode (CCM) and is the function of the input voltage, Vin, output power and a duty ratio of the switch in Discontinuous Conduction Mode (DCM).
In Automotive applications good dynamic response to changes of the input voltage and output power is desired. This is only possible, if SEPIC is running in DCM. When SEPIC input voltage decreases, at some point it is necessary, as known in previous art, to reduce SEPIC operating frequency in order to keep it running in DCM. The change of the operating frequency may cause the overshoot or undershoot of the SEPIC output voltage.
A power supply that can minimize or at least reduce the overshoot and undershoot of prior art SEPIC convertors would be an improvement over the prior art.